Conformance window information in multi-layer coding

ABSTRACT

A system and method for coding a picture in a multi-layer bitstream is disclosed. In one aspect, the method includes encoding at least one layer of the multi-layer bitstream in accordance with a first coding scheme. The multi-layer bitstream may comprise a base layer. The method further includes encoding a conformance window flag and at least one position offset for the picture in a Video Parameter Set (VPS) of the base layer. The conformance window flag may indicate that the VPS comprises the at least one position offset.

INCORPORATION BY REFERENCE TO PRIORITY APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.61/981,625, filed Apr. 18, 2014.

TECHNICAL FIELD

This disclosure relates generally to the field of video coding andcompression, and particularly to coding pictures based on conformancewindow information.

BACKGROUND Description of the Related Art

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MovingPicture Experts Group-2 (MPEG-2), MPEG-4, International TelegraphUnion-Telecommunication Standardization Sector (ITU-T) H.263, ITU-TH.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High EfficiencyVideo Coding (HEVC) standard, and extensions of such standards. Thevideo devices may transmit, receive, encode, decode, and/or storedigital video information more efficiently by implementing such videocoding techniques.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

In one aspect, there is provided a method for encoding a picture in amulti-layer bitstream that may involve encoding at least one layer ofthe multi-layer bitstream in accordance with a first coding scheme, themulti-layer bitstream comprising a base layer. The method may alsoinvolve encoding a conformance window flag and at least one positionoffset for the picture in a Video Parameter Set (VPS) of the base layer,the conformance window flag indicating that the VPS comprises the atleast one position offset.

In another aspect, there is provided an apparatus for encoding a picturein a multi-layer bitstream that may include a memory, as well as ahardware processor operationally coupled to the memory and configured toencode at least one layer of the multi-layer bitstream in accordancewith a first coding scheme, the multi-layer bitstream comprising a baselayer. The processor may be further configured to encode a conformancewindow flag and at least one position offset in a Video Parameter Set(VPS) of the base layer, wherein the conformance window flag indicatesthat the VPS comprises the at least one position offset.

In one aspect, there is provided a method for decoding a picture in amulti-layer bitstream that may involve receiving the multi-layerbitstream, the multi-layer bitstream comprising a base layer. The methodmay also involve decoding a conformance window flag and at least oneposition offset in a Video Parameter Set (VPS) of the base layer, theconformance window flag indicating that that the VPS comprises the atleast one position offset.

In yet another aspect, there is provided an apparatus for decoding apicture in a multi-layer bitstream that may include a memory, as well asa hardware processor operationally coupled to the memory and configuredto receive the multi-layer bitstream at a video codec, the multi-layerbitstream comprising a base layer. The processor may be furtherconfigured to code a conformance window flag and at least one positionoffset in a Video Parameter Set (VPS) of the base layer, wherein theconformance window flag indicates that the VPS comprises the at leastone position offset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating another example of a videoencoder that may implement techniques in accordance with aspectsdescribed in this disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating another example of a videodecoder that may implement techniques in accordance with aspectsdescribed in this disclosure.

FIG. 4 illustrates an exemplary schematic diagram illustrating atechnique for utilizing conformance window information.

FIG. 5 is a flowchart of an exemplary embodiment of a process forencoding a picture in accordance with aspect(s) described in thisdisclosure.

FIG. 6 is a flowchart of an exemplary embodiment of a process fordecoding a picture in accordance with aspect(s) described in thisdisclosure.

DETAILED DESCRIPTION

In general, this disclosure relates to coding pictures based onconformance window information in the context of advanced video codecs,such as High Efficiency Video Coding (HEVC), Advanced Video Coding(AVC), etc.

A conformance window generally refers to a window of samples of apicture in a coded video sequence that are outputted from a codingprocess. A bitstream may provide conformance window cropping parametersto indicate the output region of the coded picture. For example, awindow may be a rectangular region specified using signaled picturecoordinates. The picture coordinates may be signaled relative to areference layer.

The resulting output region specified relative to the reference layermay be used as the input for various processes, including a resamplingprocess. For example, the resampling process may utilize the conformancewindow, containing top, bottom, left, and right offsets (signaledrelative to the reference layer) to calculate the output picture.

In the Scalable extension to AVC (known as SVC) and the Scalableextension to HEVC (known as SHVC), video information may be provided inmultiple layers. The layer at the very bottom level can serve as a baselayer and the layer at the very top level can serve as an enhancementlayer. The “enhancement layer” is sometimes referred to as an “enhancedlayer,” and these terms are used interchangeably. The base layer issometimes referred to as a “reference layer,” and these terms may alsobe used interchangeably. All the layers between the top and bottomlayers may serve as both enhancement layers and base layers. Forexample, a layer in the middle can be an enhancement layer for thelayers below it, and at the same time a base layer for the layers aboveit.

In multi-layer bitstreams, layers can be coded using different codingschemes. This may occur, for instance, when a single layer is scaled toform a multi-layer bitstream. For example, an enhancement layer coded inSHVC may be combined with a base layer coded in HEVC to form amulti-layer bitstream. Because SHVC is the scalable extension of HEVC,SHVC and HEVC may be referred to as “associated” coding schemes.However, in some instances, individual layers in a multi-layer bitstreammay be coded using different coding schemes that are not associated. Forexample, a base layer coded using AVC may be combined with anenhancement layer coded using SHVC, rather than SVC (the scalableextension of AVC). In such instances, conformance window information ofthe base layer may not be available to use for various purposes, such asa resampling process. Thus, a system and method for transmitting and/orreceiving conformance window information from base layers coded using acoding scheme that is not associated with the coding scheme of the codecreceiving the reference layer is desired. Certain technologies thatprovide conformance window information for such reference layers aredescribed below.

Embodiments of the present disclosure provide systems and methods fortransmitting conformance window information using the base layer of amulti-layer bitstream. A base layer conformance window flag may be setat a codec which uses a scalable extension coding scheme when the codecreceives a base layer that was coded using a baseline coding scheme thatdoes not correspond to the scalable extension coding scheme. The flagmay indicate that base layer position offsets will follow that providepositioning information for the resampled picture. The video codec maythen utilize such information in various processes, such as theresampling process or in the other processes involving the use ofconformance window information.

While certain embodiments are described herein in the context of theHEVC and/or H.264 standards, one having ordinary skill in the art mayappreciate that systems and methods disclosed herein may be applicableto any suitable video coding standard. For example, embodimentsdisclosed herein may be applicable to one or more of the followingstandards: International Telecommunication Union (ITU) TelecommunicationStandardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263,ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4AVC), including the scalable and multiview extensions. Also, thetechniques described in this disclosure may become part of standardsdeveloped in the future. In other words, the techniques described inthis disclosure may be applicable to previously developed video codingstandards, video coding standards currently under development, andforthcoming video coding standards.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different from theunits of prediction (e.g., macroblocks) in certain previous video codingstandards. In fact, the concept of a macroblock does not exist in HEVCas understood in certain previous video coding standards. A macroblockis replaced by a hierarchical structure based on a quadtree scheme,which may provide high flexibility, among other possible benefits. Forexample, within the HEVC scheme, three types of blocks, CU, PU, andtransform unit (TU), are defined. CU may refer to the basic unit ofregion splitting. CU may be considered analogous to the concept ofmacroblock, but HEVC does not restrict the maximum size of CUs and mayallow recursive splitting into four equal size CUs to improve thecontent adaptivity. PU may be considered the basic unit of inter/intraprediction, and a single PU may contain multiple arbitrary shapepartitions to effectively code irregular image patterns. TU may beconsidered the basic unit of transform. TU can be defined independentlyfrom the PU; however, the size of a TU may be limited to the size of theCU to which the TU belongs. This separation of the block structure intothree different concepts may allow each unit to be optimized accordingto the respective role of the unit, which may result in improved codingefficiency.

For purposes of illustration only, certain embodiments disclosed hereinare described with examples including only two layers (e.g., a lowerlayer such as the base layer, and a higher layer such as the enhancementlayer) of video data. A “layer” of video data may generally refer to asequence of pictures having at least one common characteristic, such asa view, a frame rate, a resolution, or the like. For example, a layermay include video data associated with a particular view (e.g.,perspective) of multi-view video data. As another example, a layer mayinclude video data associated with a particular layer of scalable videodata. Thus, this disclosure may interchangeably refer to a layer and aview of video data. That is, a view of video data may be referred to asa layer of video data, and a layer of video data may be referred to as aview of video data. In addition, a multi-layer codec (also referred toas a multi-layer video coder or multi-layer encoder-decoder) may jointlyrefer to a multiview codec or a scalable codec (e.g., a codec configuredto encode and/or decode video data using the multiview extension to HEVC(MV-HEVC), the three-dimension extension to HEVC (3D-HEVC), SHVC, oranother multi-layer coding technique). Video encoding and video decodingmay both generally be referred to as video coding. It should beunderstood that such examples may be applicable to configurationsincluding multiple base and/or enhancement layers. In addition, for easeof explanation, the following disclosure includes the terms “frames” or“blocks” with reference to certain embodiments. However, these terms arenot meant to be limiting. For example, the techniques described belowcan be used with any suitable video units, such as blocks (e.g., CU, PU,TU, macroblocks, etc.), slices, frames, etc.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may consist of pixelsor samples arranged in horizontal and vertical lines. The number ofpixels in a single image is typically in the tens of thousands. Eachpixel typically contains luminance and chrominance information. Withoutcompression, the sheer quantity of information to be conveyed from animage encoder to an image decoder would render real-time imagetransmission impossible. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264, including the scalable and multiview extensions.

In addition, a video coding standard, namely HEVC, has been developed bythe Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T VideoCoding Experts Group (VCEG) and ISO/IEC MPEG. The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The multiview extension to HEVC, namely MV-HEVC, and thescalable extension to HEVC, named SHVC, are also being developed by theJCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video CodingExtension Development) and JCT-VC, respectively.

Video Coding System

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first,” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding. In addition to videoencoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source device 12that generates encoded video data to be decoded at a later time by adestination device 14. In the example of FIG. 1A, the source device 12and destination device 14 constitute separate devices. It is noted,however, that the source device 12 and destination device 14 may be onor part of the same device, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source device 12 and thedestination device 14 may respectively comprise any of a wide range ofdevices, including desktop computers, notebook (e.g., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In various embodiments, the source device 12 andthe destination device 14 may be equipped for wireless communication.

The destination device 14 may receive, via link 16, the encoded videodata to be decoded. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source device12 to the destination device 14. In the example of FIG. 1A, the link 16may comprise a communication medium to enable the source device 12 totransmit encoded video data to the destination device 14 in real-time.The encoded video data may be modulated according to a communicationstandard, such as a wireless communication protocol, and transmitted tothe destination device 14. The communication medium may comprise anywireless or wired communication medium, such as a radio frequency (RF)spectrum or one or more physical transmission lines. The communicationmedium may form part of a packet-based network, such as a local areanetwork, a wide-area network, or a global network such as the Internet.The communication medium may include routers, switches, base stations,or any other equipment that may be useful to facilitate communicationfrom the source device 12 to the destination device 14.

Alternatively, encoded data may be output from an output interface 22 toan a storage device 31 (optionally present). Similarly, encoded data maybe accessed from the storage device 31 by an input interface 28, forexample, of the destination device 14. The storage device 31 may includeany of a variety of distributed or locally accessed data storage mediasuch as a hard drive, flash memory, volatile or non-volatile memory, orany other suitable digital storage media for storing encoded video data.In a further example, the storage device 31 may correspond to a fileserver or another intermediate storage device that may hold the encodedvideo generated by the source device 12. The destination device 14 mayaccess stored video data from the storage device 31 via streaming ordownload. The file server may be any type of server capable of storingencoded video data and transmitting that encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), a File Transfer Protocol (FTP) server, network attachedstorage (NAS) devices, or a local disk drive. The destination device 14may access the encoded video data through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a wireless local area network (WLAN) connection), a wiredconnection (e.g., a digital subscriber line (DSL), a cable modem, etc.),or a combination of both that is suitable for accessing encoded videodata stored on a file server. The transmission of encoded video datafrom the storage device 31 may be a streaming transmission, a downloadtransmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HypertextTransfer Protocol (HTTP), etc.), encoding of digital video for storageon a data storage medium, decoding of digital video stored on a datastorage medium, or other applications. In some examples, video codingsystem 10 may be configured to support one-way or two-way videotransmission to support applications such as video streaming, videoplayback, video broadcasting, and/or video telephony.

In the example of FIG. 1A, the source device 12 includes a video source18, video encoder 20 and the output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source device 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source device 12 and the destination device 14 mayform so-called “camera phones” or “video phones”, as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitted tothe destination device 14 via the output interface 22 of the sourcedevice 12. The encoded video data may also (or alternatively) be storedonto the storage device 31 for later access by the destination device 14or other devices, for decoding and/or playback. The video encoder 20illustrated in FIGS. 1A and 1B may comprise the video encoder 20illustrated FIG. 2A, the video encoder 23 illustrated in FIG. 2B, or anyother video encoder described herein.

In the example of FIG. 1A, the destination device 14 includes the inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination device 14 may receive the encodedvideo data over the link 16 and/or from the storage device 31. Theencoded video data communicated over the link 16, or provided on thestorage device 31, may include a variety of syntax elements generated bythe video encoder 20 for use by a video decoder, such as the videodecoder 30, in decoding the video data. Such syntax elements may beincluded with the encoded video data transmitted on a communicationmedium, stored on a storage medium, or stored a file server. The videodecoder 30 illustrated in FIGS. 1A and 1B may comprise the video decoder30 illustrated FIG. 3A, the video decoder 33 illustrated in FIG. 3B, orany other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination device 14. In some examples, the destination device 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationdevice 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video coding system 10′wherein the source device 12 and the destination device 14 are on orpart of a device 11. The device 11 may be a telephone handset, such as a“smart” phone or the like. The device 11 may include acontroller/processor device 13 (optionally present) in operativecommunication with the source device 12 and the destination device 14.The video coding system 10′ of FIG. 1B, and components thereof, areotherwise similar to the video coding system 10 of FIG. 1A, andcomponents thereof.

The video encoder 20 and the video decoder 30 may operate according to avideo compression standard, such as HEVC, and may conform to a HEVC TestModel (HM). Alternatively, the video encoder 20 and the video decoder 30may operate according to other proprietary or industry standards, suchas the ITU-T H.264 standard, alternatively referred to as MPEG-4, Part10, AVC, or extensions of such standards. The techniques of thisdisclosure, however, are not limited to any particular coding standard.Other examples of video compression standards include MPEG-2 and ITU-TH.263.

Although not shown in the examples of FIGS. 1A and 1B, the video encoder20 and the video decoder 30 may each be integrated with an audio encoderand decoder, and may include appropriate MUX-DEMUX units, or otherhardware and software, to handle encoding of both audio and video in acommon data stream or separate data streams. If applicable, in someexamples, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder in a respective device.

Video Coding Process

As mentioned briefly above, the video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When the video encoder 20 encodes thevideo data, the video encoder 20 may generate a bitstream. The bitstreammay include a sequence of bits that form a coded representation of thevideo data. The bitstream may include coded pictures and associateddata. A coded picture is a coded representation of a picture.

To generate the bitstream, the video encoder 20 may perform encodingoperations on each picture in the video data. When the video encoder 20performs encoding operations on the pictures, the video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include video parameter sets (VPS), sequence parameter sets(SPSs), picture parameter sets (PPSs), adaptation parameter sets (APSs),and other syntax structures. An SPS may contain parameters applicable tozero or more sequences of pictures. A PPS may contain parametersapplicable to zero or more pictures. An APS may contain parametersapplicable to zero or more pictures. Parameters in an APS may beparameters that are more likely to change than parameters in a PPS.

To generate a coded picture, the video encoder 20 may partition apicture into equally-sized video blocks. A video block may be atwo-dimensional array of samples. Each of the video blocks is associatedwith a treeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more coding units (CUs). The video encoder 20 may usequadtree partitioning to partition the video blocks of treeblocks intovideo blocks associated with CUs, hence the name “treeblocks.”

In some examples, the video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, the videoencoder 20 may perform encoding operations on each slice of the picture.When the video encoder 20 performs an encoding operation on a slice, thevideo encoder 20 may generate encoded data associated with the slice.The encoded data associated with the slice may be referred to as a“coded slice.”

To generate a coded slice, the video encoder 20 may perform encodingoperations on each treeblock in a slice. When the video encoder 20performs an encoding operation on a treeblock, the video encoder 20 maygenerate a coded treeblock. The coded treeblock may comprise datarepresenting an encoded version of the treeblock.

When the video encoder 20 generates a coded slice, the video encoder 20may perform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, the video encoder20 may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on until thevideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, the video encoder 20may be able to access information generated by encoding treeblocks aboveand to the left of the given treeblock when encoding the giventreeblock. However, the video encoder 20 may be unable to accessinformation generated by encoding treeblocks below and to the right ofthe given treeblock when encoding the given treeblock.

To generate a coded treeblock, the video encoder 20 may recursivelyperform quadtree partitioning on the video block of the treeblock todivide the video block into progressively smaller video blocks. Each ofthe smaller video blocks may be associated with a different CU. Forexample, the video encoder 20 may partition the video block of atreeblock into four equally-sized sub-blocks, partition one or more ofthe sub-blocks into four equally-sized sub-sub-blocks, and so on. Apartitioned CU may be a CU whose video block is partitioned into videoblocks associated with other CUs. A non-partitioned CU may be a CU whosevideo block is not partitioned into video blocks associated with otherCUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times the video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

The video encoder 20 may perform encoding operations on (e.g., encode)each CU of a treeblock according to a z-scan order. In other words, thevideo encoder 20 may encode a top-left CU, a top-right CU, a bottom-leftCU, and then a bottom-right CU, in that order. When the video encoder 20performs an encoding operation on a partitioned CU, the video encoder 20may encode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, the videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, the video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, the video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When the video encoder 20 encodes a non-partitioned CU, the videoencoder 20 may generate one or more prediction units (PUs) for the CU.Each of the PUs of the CU may be associated with a different video blockwithin the video block of the CU. The video encoder 20 may generate apredicted video block for each PU of the CU. The predicted video blockof a PU may be a block of samples. The video encoder 20 may use intraprediction or inter prediction to generate the predicted video block fora PU.

When the video encoder 20 uses intra prediction to generate thepredicted video block of a PU, the video encoder 20 may generate thepredicted video block of the PU based on decoded samples of the pictureassociated with the PU. If the video encoder 20 uses intra prediction togenerate predicted video blocks of the PUs of a CU, the CU is anintra-predicted CU. When the video encoder 20 uses inter prediction togenerate the predicted video block of the PU, the video encoder 20 maygenerate the predicted video block of the PU based on decoded samples ofone or more pictures other than the picture associated with the PU. Ifthe video encoder 20 uses inter prediction to generate predicted videoblocks of the PUs of a CU, the CU is an inter-predicted CU.

Furthermore, when the video encoder 20 uses inter prediction to generatea predicted video block for a PU, the video encoder 20 may generatemotion information for the PU. The motion information for a PU mayindicate one or more reference blocks of the PU. Each reference block ofthe PU may be a video block within a reference picture. The referencepicture may be a picture other than the picture associated with the PU.In some instances, a reference block of a PU may also be referred to asthe “reference sample” of the PU. The video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After the video encoder 20 generates predicted video blocks for one ormore PUs of a CU, the video encoder 20 may generate residual data forthe CU based on the predicted video blocks for the PUs of the CU. Theresidual data for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, the video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with transform units (TUs) of the CU. Each TUof a CU may be associated with a different residual video block.

The video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, the video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

The video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how thevideo encoder 20 quantizes transform coefficient blocks associated withthe CU. The video encoder 20 may adjust the degree of quantizationapplied to the transform coefficient blocks associated with a CU byadjusting the QP value associated with the CU.

After the video encoder 20 quantizes a transform coefficient block, thevideo encoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block. Thevideo encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such ascontext-adaptive variable-length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by the video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, Supplemental EnhancementInformation (SEI), an access unit delimiter, filler data, or anothertype of data. The data in a NAL unit may include various syntaxstructures.

The video decoder 30 may receive the bitstream generated by the videoencoder 20. The bitstream may include a coded representation of thevideo data encoded by the video encoder 20. When the video decoder 30receives the bitstream, the video decoder 30 may perform a parsingoperation on the bitstream. When the video decoder 30 performs theparsing operation, the video decoder 30 may extract syntax elements fromthe bitstream. The video decoder 30 may reconstruct the pictures of thevideo data based on the syntax elements extracted from the bitstream.The process to reconstruct the video data based on the syntax elementsmay be generally reciprocal to the process performed by the videoencoder 20 to generate the syntax elements.

After the video decoder 30 extracts the syntax elements associated witha CU, the video decoder 30 may generate predicted video blocks for thePUs of the CU based on the syntax elements. In addition, the videodecoder 30 may inverse quantize transform coefficient blocks associatedwith TUs of the CU. The video decoder 30 may perform inverse transformson the transform coefficient blocks to reconstruct residual video blocksassociated with the TUs of the CU. After generating the predicted videoblocks and reconstructing the residual video blocks, the video decoder30 may reconstruct the video block of the CU based on the predictedvideo blocks and the residual video blocks. In this way, the videodecoder 30 may reconstruct the video blocks of CUs based on the syntaxelements in the bitstream.

Video Encoder

FIG. 2A is a block diagram illustrating an example of the video encoder20 that may implement techniques in accordance with aspects described inthis disclosure. The video encoder 20 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videoencoder 20 may be configured to perform any or all of the techniques ofthis disclosure. In some examples, the techniques described in thisdisclosure may be shared among the various components of the videoencoder 20. In some examples, additionally or alternatively, a processor(not shown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

For purposes of explanation, this disclosure describes the video encoder20 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2A is for a single layer codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing of a multi-layercodec.

The video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2A, the video encoder 20 includes a plurality offunctional components. The functional components of the video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, the video encoder 20may include more, fewer, or different functional components.Furthermore, motion estimation unit 122 and motion compensation unit 124may be highly integrated, but are represented in the example of FIG. 2Aseparately for purposes of explanation.

The video encoder 20 may receive video data. The video encoder 20 mayreceive the video data from various sources. For example, the videoencoder 20 may receive the video data from video source 18 (e.g., shownin FIG. 1A or 1B) or another source. The video data may represent aseries of pictures. To encode the video data, the video encoder 20 mayperform an encoding operation on each of the pictures. As part ofperforming the encoding operation on a picture, the video encoder 20 mayperform encoding operations on each slice of the picture. As part ofperforming an encoding operation on a slice, the video encoder 20 mayperform encoding operations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally-sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

The video encoder 20 may perform encoding operations on eachnon-partitioned CU of a treeblock. When the video encoder 20 performs anencoding operation on a non-partitioned CU, the video encoder 20generates data representing an encoded representation of thenon-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. The video encoder 20 and the video decoder 30 maysupport various PU sizes. Assuming that the size of a particular CU is2N×2N, the video encoder 20 and the video decoder 30 may support PUsizes of 2N×2N or N×N, and inter-prediction in symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, 2N×nU, nL×2N, nR×2N, or similar. The videoencoder 20 and the video decoder 30 may also support asymmetricpartitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N. In someexamples, prediction processing unit 100 may perform geometricpartitioning to partition the video block of a CU among PUs of the CUalong a boundary that does not meet the sides of the video block of theCU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples, that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to the video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. The video decoder30 may use the motion vector of the indicated neighboring PU and themotion vector difference to determine the motion vector of the PU. Byreferring to the motion information of a first PU when signaling themotion information of a second PU, the video encoder 20 may be able tosignal the motion information of the second PU using fewer bits.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it may be probable that the selected intra prediction modeis the same as the intra prediction mode of a neighboring PU. In otherwords, the intra prediction mode of the neighboring PU may be the mostprobable mode for the current PU. Thus, prediction processing unit 100may generate a syntax element to indicate that the selected intraprediction mode is the same as the intra prediction mode of theneighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SHVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

The video encoder 20 may associate a QP value with a CU in various ways.For example, the video encoder 20 may perform a rate-distortion analysison a treeblock associated with the CU. In the rate-distortion analysis,the video encoder 20 may generate multiple coded representations of thetreeblock by performing an encoding operation multiple times on thetreeblock. The video encoder 20 may associate different QP values withthe CU when the video encoder 20 generates different encodedrepresentations of the treeblock. The video encoder 20 may signal that agiven QP value is associated with the CU when the given QP value isassociated with the CU in a coded representation of the treeblock thathas a lowest bitrate and distortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, the videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of the video encoder 20. For example, entropy encoding unit116 may receive transform coefficient blocks from quantization unit 106and may receive syntax elements from prediction processing unit 100.When entropy encoding unit 116 receives the data, entropy encoding unit116 may perform one or more entropy encoding operations to generateentropy encoded data. For example, the video encoder 20 may perform aCAVLC operation, a CABAC operation, a variable-to-variable (V2V) lengthcoding operation, a syntax-based context-adaptive binary arithmeticcoding (SBAC) operation, a Probability Interval Partitioning Entropy(PIPE) coding operation, or another type of entropy encoding operationon the data. Entropy encoding unit 116 may output a bitstream thatincludes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating another example of a multi-layervideo encoder 23 (also simply referred to as video encoder 23) that mayimplement techniques in accordance with aspects described in thisdisclosure. The video encoder 23 may be configured to processmulti-layer video frames, such as for SHVC and MV-HEVC. Further, thevideo encoder 23 may be configured to perform any or all of thetechniques of this disclosure.

The video encoder 23 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 and may performthe functions described above with respect to the video encoder 20.Further, as indicated by the reuse of reference numbers, the videoencoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 23 isillustrated as including two video encoders 20A and 20B, the videoencoder 23 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 23 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 23 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 23 mayinclude a resampling unit 90. The resampling unit 90 may, in some cases,upsample a base layer of a received video frame to, for example, createan enhancement layer. The resampling unit 90 may upsample particularinformation associated with the received base layer of a frame, but notother information. For example, the resampling unit 90 may upsample thespatial size or number of pixels of the base layer, but the number ofslices or the picture order count may remain constant. In some cases,the resampling unit 90 may not process the received video and/or may beoptional. For example, in some cases, the prediction processing unit 100may perform upsampling. In some embodiments, the resampling unit 90 isconfigured to upsample a layer and reorganize, redefine, modify, oradjust one or more slices to comply with a set of slice boundary rulesand/or raster scan rules. Although primarily described as upsampling abase layer, or a lower layer in an access unit, in some cases, theresampling unit 90 may downsample a layer. For example, if duringstreaming of a video bandwidth is reduced, a frame may be downsampledinstead of upsampled.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 100 of a higher layer encoder (e.g., the video encoder 20B)configured to encode a picture in the same access unit as the lowerlayer encoder. In some cases, the higher layer encoder is one layerremoved from the lower layer encoder. In other cases, there may be oneor more higher layer encoders between the layer 0 video encoder and thelayer 1 encoder of FIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 114 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the prediction processing unit 100 of thevideo encoder 20B. For example, if video data provided to the videoencoder 20B and the reference picture from the decoded picture buffer114 of the video encoder 20A are of the same size or resolution, thereference picture may be provided to the video encoder 20B without anyresampling.

In some embodiments, the video encoder 23 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before providing the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 23 may further include amultiplexor (or mux) 98. The mux 98 can output a combined bitstream fromthe video encoder 23. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 23, such as from a processor on a sourcedevice including the source device 12. The control signal may begenerated based on the resolution or bitrate of a video from the videosource 18, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionoutput desired from the video encoder 23.

Video Decoder

FIG. 3A is a block diagram illustrating an example of the video decoder30 that may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videodecoder 30 may be configured to perform any or all of the techniques ofthis disclosure. In some examples, the techniques described in thisdisclosure may be shared among the various components of the videodecoder 30. In some examples, additionally or alternatively, a processor(not shown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

For purposes of explanation, this disclosure describes the video decoder30 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3A is for a single layer codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing of a multi-layercodec.

In the example of FIG. 3A, the video decoder 30 includes a plurality offunctional components. The functional components of the video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, the video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 20 of FIG. 2A. In other examples, the video decoder 30 mayinclude more, fewer, or different functional components.

The video decoder 30 may receive a bitstream that comprises encodedvideo data. The bitstream may include a plurality of syntax elements.When the video decoder 30 receives the bitstream, entropy decoding unit150 may perform a parsing operation on the bitstream. As a result ofperforming the parsing operation on the bitstream, entropy decoding unit150 may extract syntax elements from the bitstream. As part ofperforming the parsing operation, entropy decoding unit 150 may entropydecode entropy encoded syntax elements in the bitstream. Predictionprocessing unit 152, inverse quantization unit 154, inverse transformunit 156, reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL units, entropydecoding unit 150 may perform parsing operations that extract syntaxelements from coded CUs in the slice data. The extracted syntax elementsmay include syntax elements associated with transform coefficientblocks. Entropy decoding unit 150 may then perform CABAC decodingoperations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, the video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, the video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, the video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by the video encoder 20for a CU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from the video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by the video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by the video encoder 20 according toreceived syntax information and use the interpolation filters to producethe predicted video block.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, the video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the enhancement layer)using one or more different layers that are available in SHVC (e.g., abase or reference layer). Such prediction may be referred to asinter-layer prediction. Inter-layer prediction unit 166 utilizesprediction methods to reduce inter-layer redundancy, thereby improvingcoding efficiency and reducing computational resource requirements. Someexamples of inter-layer prediction include inter-layer intra prediction,inter-layer motion prediction, and inter-layer residual prediction.Inter-layer intra prediction uses the reconstruction of co-locatedblocks in the base layer to predict the current block in the enhancementlayer. Inter-layer motion prediction uses motion information of the baselayer to predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, the videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,filter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, the video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, the video decoder 30 may perform, based on thevideo blocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating another example of a multi-layervideo decoder 33 (also simply referred to as video decoder 33) that mayimplement techniques in accordance with aspects described in thisdisclosure. The video decoder 33 may be configured to processmulti-layer video frames, such as for SHVC and multiview coding.Further, the video decoder 33 may be configured to perform any or all ofthe techniques of this disclosure.

The video decoder 33 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 and may performthe functions described above with respect to the video decoder 30.Further, as indicated by the reuse of reference numbers, the videodecoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 33 isillustrated as including two video decoders 30A and 30B, the videodecoder 33 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 33 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 33 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 33 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the decoded picturebuffer 160. In some embodiments, the upsampling unit 92 can include someor all of the embodiments described with respect to the resampling unit90 of FIG. 2A. In some embodiments, the upsampling unit 92 is configuredto upsample a layer and reorganize, redefine, modify, or adjust one ormore slices to comply with a set of slice boundary rules and/or rasterscan rules. In some cases, the upsampling unit 92 may be a resamplingunit configured to upsample and/or downsample a layer of a receivedvideo frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 160 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 152 of a higher layer decoder (e.g., the video decoder 30B)configured to decode a picture in the same access unit as the lowerlayer decoder. In some cases, the higher layer decoder is one layerremoved from the lower layer decoder. In other cases, there may be oneor more higher layer decoders between the layer 0 decoder and the layer1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 160 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the prediction processing unit 152 of thevideo decoder 30B. For example, if video data provided to the videodecoder 30B and the reference picture from the decoded picture buffer160 of the video decoder 30A are of the same size or resolution, thereference picture may be provided to the video decoder 30B withoutupsampling. Further, in some embodiments, the upsampling unit 92 may bea resampling unit 90 configured to upsample or downsample a referencepicture received from the decoded picture buffer 160 of the videodecoder 30A.

As illustrated in FIG. 3B, the video decoder 33 may further include ademultiplexor (or demux) 99. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 33, such as from a processor on a destination deviceincluding the destination device 14. The control signal may be generatedbased on the resolution or bitrate of a video from the input interface28, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionobtainable by the video decoder 33.

Intra Random Access Point (IRAP) Pictures

Some video coding schemes may provide various random access pointsthroughout the bitstream such that the bitstream may be decoded startingfrom any of those random access points without needing to decode anypictures that precede those random access points in the bitstream. Insuch video coding schemes, all pictures that follow a random accesspoint in decoding order, except random access skipped leading (RASL)pictures, can be correctly decoded without using any pictures thatprecede the random access point. For example, even if a portion of thebitstream is lost during transmission or during decoding, a decoder canresume decoding the bitstream starting from the next random accesspoint. Support for random access may facilitate, for example, dynamicstreaming services, seek operations, channel switching, etc.

In some coding schemes, such random access points may be provided bypictures that are referred to as intra random access point (IRAP)pictures. For example, a random access point associated with anenhancement layer IRAP picture in an enhancement layer (“layerA”) thatis contained in an access unit (“auA”) may provide layer-specific randomaccess such that for each reference layer (“layerB”) of layerA (e.g., areference layer being a layer that is used to predict layerA) having arandom access point associated with a picture contained in an accessunit (“auB”) that is in layerB and precedes auA in decoding order (or arandom access point contained in auA), the pictures in layerA thatfollow auA in decoding order (including those pictures located in auA),are correctly decodable without needing to decode any pictures in layerAthat precede auA.

IRAP pictures may be coded using intra prediction (e.g., coded withoutreferring to other pictures) and/or inter-layer prediction, and mayinclude, for example, instantaneous decoder refresh (IDR) pictures,clean random access (CRA) pictures, and broken link access (BLA)pictures. When there is an IDR picture in the bitstream, all thepictures that precede the IDR picture in decoding order are not used forprediction by pictures that follow the IDR picture. When there is a CRApicture in the bitstream, the pictures that follow the CRA picture mayor may not use pictures that precede the CRA picture in decoding orderfor prediction. Those pictures that follow the CRA picture in decodingorder but use pictures that precede the CRA picture in decoding ordermay be referred to as RASL pictures. Another type of picture that canfollow an IRAP picture in decoding order and precede the IRAP picture inoutput order is a random access decodable leading (RADL) picture, whichmay not contain references to any pictures that precede the IRAP picturein decoding order. RASL pictures may be discarded by the decoder if thepictures that precede the CRA picture are not available. A BLA pictureindicates to the decoder that pictures that precede the BLA picture maynot be available to the decoder (e.g., because two bitstreams arespliced together and the BLA picture is the first picture of the secondbitstream in decoding order). An access unit (e.g., a group of picturesconsisting of all the coded pictures associated with the same outputtime across multiple layers) containing a base layer picture (e.g.,having a layer ID value of 0) that is an IRAP picture may be referred toas an IRAP access unit.

Resampling Process in SHVC

In a resampling process, the number of samples of a picture can beupsampled (increased) or downsampled (decreased). In one design ofreference layer picture resampling, an output reference layer picture isused as the input for the resampling process.

In SHVC, if a reference layer (or base layer) picture size is differentfrom the enhancement layer picture size, a resampling (or upsampling)process can be applied to the reference layer picture to match the sizeof the enhancement layer picture for inter-layer prediction. To resamplethe reference layer picture, an N tap resampling filter can be appliedfor each color component.

In the filtering process, the samples (or pixels) magnitudes of thereference layer picture can be multiplied by filter coefficients andsummed up to derive a filtered sample (or pixel). Since the size of thereference layer picture and the size of the enhancement layer pictureare different, the coordinates of the reference layer samples involvedin the filtering process may be defined. For example, the samplelocation of the reference layer picture that corresponds to the samplelocation of the current enhancement layer picture can be determined sothat the sample(s) indicated by the sample location of the referencelayer picture can be used in the resampling process.

Conformance Window for the Base Layer

As noted above, conformance window information may be included in areference layer and may be used for a variety of purposes, includingresampling processes. Conformance window cropping parameters are used toindicate the output region of a coded picture.

FIG. 4 illustrates an exemplary schematic diagram illustrating atechnique for utilizing conformance window information. Coded data,including SPS, PPS, and VPS, is stored at the Coded Picture Buffer (CPB)405. The SPS may include parameters for describing the characteristicsof the coded sequence, such as profile, tier, and level indications. Inconventional systems, conformance window cropping parameters may also beincluded in the SPS. This information is provided to the decodingprocess 410, and the decoded pictures are stored for output and used asreference pictures in the Decoded Picture Buffer (DPB) 415. The decodedpictures are then passed to the output cropping stage 420 where outputcropping is applied to the output pictures according to the conformancewindow parameters specified in the SPS.

Table 1 below shows a conventional system for signaling a conformancewindow in HEVC. As shown in Table 1, below, a conformance window mayinclude top, bottom, left, and/or right offsets. These offsets may beused to indicate which samples in a picture are to be used forresampling.

TABLE 1 Conformance window flags in HEVC conformance_window_flag u(1)if( conformance_window_flag ) { conf_win_left_offset ue(v)conf_win_right_offset ue(v) conf_win_top_offset ue(v)conf_win_bottom_offset ue(v) }

For single-layer bitstreams, a conformance window may be signaled in theSPS. However, for multi-layer bitstreams, it may be advantageous tosignal the base layer in the VPS because the VPS applies to all of thelayers of a multi-layer bitstream.

In multi-layer bitstreams, individual layers may be coded usingdifferent coding schemes, such as HEVC, SHVC, MV-HEVC, 3D-HEVC, AVC,SVC, etc. Some of these coding schemes may be associated with othercoding schemes. For example, SHVC, as the scalable extension of HEVC,may be associated with HEVC. However, SHVC and/or HEVC may be associatedwith other coding schemes. When a codec receives a bitstream having areference layer that was coded using a coding scheme the codec is notassociated with, the codec may not be suited to determine conformancewindow information for the layer. In an example, the conformance windowflags in HEVC, shown in Table 1 above, may be suitable for use by acodec using SHVC but not by a codec using SVC. Moreover, in the presentexample, conformance window flags in HEVC, shown in Table 1 above, maynot be suitable for conveying conformance window information to an SVCcodec. Conformance window information for a base layer that was codedusing a single layer coding scheme may not be signaled and thus may notbe available for a codec using an extension coding scheme that is notassociated with the single layer coding scheme.

There are two resampling processes in SHVC: (1) sample or pixelinformation resampling and (2) motion (i.e., motion field) or non-pixelinformation resampling. Embodiments of the present disclosure may beapplicable to one, both, or neither of these resampling processes.

In some aspects of the present disclosure, conformance windowinformation may be applied to calculate scalability aspect ratio orscaling factor. For example, a resampling process may be applied to adecoded reference layer picture with the calculated aspect ratio. Inother aspects of the present disclosure, the resampling process may usean output reference layer picture as an input for the resamplingprocess. Embodiments of the present disclosure may apply to one, both,or neither of these aspects.

Embodiments of the present disclosure provide flags for signalingconformance window information in a base layer. A base layer conformancewindow may be signaled, for example, in VPS, SPS, PPS, and/or the sliceheader. In some embodiments, the base layer conformance window may besignaled (e.g., may only be signaled) when the base layer is indicatedto have been encoded using a coding scheme that is not associated withthe receiving codec and/or a coding scheme used by an encoder. Forexample, the base layer conformance window may be signaled based on anindication that the base layer is coded using a non-HEVC coding scheme(e.g., AVC, which is a coding scheme that may not be associated withSHVC) when it is received by an SHVC compliant decoder. Exemplary syntaxand semantics for signaling the base layer conformance window is shownbelow in Table 2.

TABLE 2 Conformance window flags for the base layerbl_conformance_window_flag u(1) if( bl_conformance_window_flag ) {bl_conf_win_left_offset ue(v) bl_conf_win_right_offset ue(v)bl_conf_win_top_offset ue(v) bl_conf_win_bottom_offset ue(v) }

In Table 2, bl_conformance_window_flag may be set to 1 to indicate thatoffset parameters of the base layer follow after. Otherwise,bl_conformance_window_flag being set to 0 may indicate that the offsetparameters are not present. If bl_conformance_window_flag is notpresent, it may be inferred to be set to 0. In some embodiments, abitstream constraint requirement may be used. For example,bl_conformance_window_flag may be set to 1 for any non-HEVC coded baselayer. In another example, bl_conformance_window_flag may be set to 1 ifthe base layer has been coded using a coding scheme that is notassociated with the receiving codec.

Further, in Table 2, bl_conf_win_left_offset, bl_conf_win_right_offset,bl_conf_win_top_offset, and bl_conf_win_bottom_offset may specify thesamples of the base layer picture in the Coded Video Sequence (CVS) thatare outputted from the base layer decoding process, in terms of arectangular region specified in picture coordinates for the output. Whenbl_conformance_window_flag is equal to 0, the values ofbl_conf_win_left_offset, bl_conf_win_right_offset,bl_conf_win_top_offset, and bl_conf_win_bottom_offset may be inferred toalso be equal to 0.

In one example, the signaled base layer window offsets may be includedto calculate the output base layer picture size and, optionally, alocation relative to the decoded base layer picture to be used in theresampling process, and to calculate the scalability aspect ratio orscaling factor, for example as the fraction of the output base layerwidth or height relative the decoded enhancement layer width or height,respectively.

FIG. 5 is a flowchart of an exemplary embodiment of a process forencoding a picture in accordance with aspect(s) of the presentdisclosure. The process 500 starts at block 505.

At block 510, the process 500 may involve encoding layers of amulti-layer bitstream. In some embodiments, a first video encoder mayencode all layers of the multi-layer bitstream. In other embodiments,the video encoder may encode only a portion of the layers of themulti-layer bitstream. A video encoder may encode layers of a bitstreamin accordance with a coding scheme. In some aspects, the bitstream mayinclude a base layer that has been coded using a coding scheme that isdifferent from and/or not associated with the coding scheme used by thefirst video encoder. For example, the base layer may have been encodedby a second video encoder that is different from the first videoencoder. In other aspects, the bitstream may include a base layer thathas been coded using a coding scheme that is the same as and/or isassociated with the receiving codec. For example, the base layer mayhave been encoded by the first video encoder.

At decision block 515, the process 500 may involve determining whetherthe base layer has been encoded using a coding scheme that is associatedwith the coding scheme used by the first video encoder. If the baselayer has been encoded using a coding scheme that is associated with thecoding scheme used by the first video encoder, the process 500 mayinvolve proceeding to block 520. If the base layer has been encodedusing a coding scheme that is not associated with the coding scheme usedby the first video encoder, the process 500 may involve proceeding todecision block 535.

At block 520, the process 500 may involve signaling a conformancewindow. In one example, signaling the conformance window may involvesetting a conformance window flag to a value (e.g., 1) to indicate thatposition offsets will follow that provide positioning information forthe resampled picture. A conformance window may include one or moreoffsets, for example top, bottom, left, and right offsets (see, e.g.,Table 1). The conformance window and/or offsets may be signaled in anSPS. For example, the conformance window may be signaled in an HEVCcoded layer.

At block 525, the process 500 may involve encoding the picture using theconformance window information.

At block 530, If the base layer has been encoded using a coding schemethat is not associated with the coding scheme used by the first videoencoder, the process 500 may involve signaling a base layer conformancewindow. In one example, signaling the conformance window may involvesetting a base layer conformance window flag to a value (e.g., 1) toindicate that base layer position offsets will follow that providepositioning information for the resampled picture. A base layerconformance window may include one or more offsets, for example top,bottom, left, and right offsets (see, e.g., Table 2). The conformancewindow and/or offsets may be signaled in a VPS, SPS, PPS, and/or sliceheader.

At block 535, the process 500 may involve coding the picture using thebase layer conformance window. The process 500 ends at block 540.

FIG. 6 is a flowchart of an exemplary embodiment of a process fordecoding a picture in accordance with aspect(s) described in thisdisclosure. The process 600 starts at block 605.

At block 610, the process 600 may involve receiving a bitstream. In someaspects, the bitstream may include a base layer that has been codedusing a coding scheme that is not associated with a coding scheme usedto encode other layers of the bitstream. In other aspects, the bitstreammay include a base layer that has been coded using a coding scheme thatis associated with a coding scheme used to encode other layers of thebitstream.

At block 615, the process 600 may involve decoding a conformance windowflag and at least one position offset in the base layer of thebitstream. In some embodiments, the conformance window flag and/or theat least one position offset may be signaled in the VPS of the baselayer.

At block 620, the process 600 may involve decoding the picture using thebase layer conformance window. The process 600 ends at block 625.

In one aspect, the base layer output picture may be derived for numerouspurposes, including displaying base layer pictures and performingresampling processes.

In another aspect, size of a conformance window may be signaledexplicitly with width and height information, and the width and heightinformation can be used to calculate a scalability aspect ratio. Thismay be done with or without determining a decoded picture size or anexact positioning of the output base layer picture. Thus, theconformance window may be only partially signaled.

In a further aspect, if a received base layer is non-HEVC coded,semantics of scaled reference offsets and the resampling process used inSHVC working drafts may be modified such that a reference layer decodedpicture with applied scaled reference offsets may be used as an inputinto the resampling process and/or scalability ratio calculation. Forexample, in such aspects, scaled reference offsets may includescaled_ref_layer_left_offset, scaled_ref_layer_top_offset,scaled_ref_layer_right_offset, and scaled_ref_layer_bottom_offset.

In yet another aspect, an SHVC decoder may use an AVC SPS syntaxstructure such that conformance window information of an AVC base layermay be used by the SHVC enhancement layers and can be used to deriveconformance window information without any additional signaling.

In still another aspect, values of conformance window parameters of abase layer may be provided by external means (e.g., by system level),instead of signaling a related syntax in the SHVC bitstream. This may bedone as in a similar way as with the base layer itself and otherexternally provided parameters for base layer pictures.

Other Considerations

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, and algorithm steps describedin connection with the embodiments disclosed herein may be implementedas electronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas devices or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software or hardware configured for encoding and decoding, orincorporated in a combined video encoder-decoder (CODEC). Also, thetechniques could be fully implemented in one or more circuits or logicelements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components, orunits are described in this disclosure to emphasize functional aspectsof devices configured to perform the disclosed techniques, but do notnecessarily require realization by different hardware units. Rather, asdescribed above, various units may be combined in a codec hardware unitor provided by a collection of inter-operative hardware units, includingone or more processors as described above, in conjunction with suitablesoftware and/or firmware.

Although the foregoing has been described in connection with variousdifferent embodiments, features or elements from one embodiment may becombined with other embodiments without departing from the teachings ofthis disclosure. For example, an encoder may have multiple of thediscussed hash functions available for use, and may determine which hashfunction to use for each block of video information. A stored hash indexmay comprise multiple values, and a block of video information may bemapped to the stored hash index if the computed hash index for the blockmatches one or more of the values of the stored hash index. Thediscussed hash filters may instead be applied in combination withautomatic addition of a current block to a hash table, i.e., a hashfilter may be applied after information indicative of a block of videoinformation is added to the hash table. For example, if a linked listbecomes full, then hash filters may be applied at that point. Similarcombinations of features are also contemplated including addinginformation indicative of a current block to a hash table after theinformation has been mapped to a hash index in the hash table; however,the combinations of features between the respective embodiments are notnecessarily limited thereto.

Various embodiments of the disclosure have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. A method for encoding a picture in a multi-layerbitstream, comprising: encoding at least one enhancement layer of themulti-layer bitstream based on a first coding scheme, the multi-layerbitstream comprising a base layer different from the enhancement layer;determining whether the base layer was coded based on the first codingscheme or a coding scheme associated with the first coding scheme;encoding a conformance window flag in a Video Parameter Set (VPS) of thebase layer, the conformance window flag indicating whether the VPScomprises at least one position offset, the at least one position offsetindicative of positioning information for the picture; and in responseto determining that the base layer was coded based on the first codingscheme or a coding scheme associated with the first coding scheme,setting the conformance window flag to a first predetermined value, orin response to determining that the base layer was not coded based onthe first coding scheme or a coding scheme associated with the firstcoding scheme: (i) setting conformance window flag to a secondpredetermined value different from the first predetermined value, thesecond predetermined value indicating the VPS comprises the at least oneposition offset, and (ii) encoding the at least one position offset inthe VPS of the base layer.
 2. The method of claim 1, wherein the codingscheme is associated with the first coding scheme only if the codingscheme is identical to the first coding scheme.
 3. The method of claim1, wherein the coding scheme is associated with the first coding schemeonly if the first coding scheme is a scalable extension of the codingscheme.
 4. The method of claim 1, wherein the at least one positionoffset comprises at least one of a left offset, a right offset, a topoffset, and a bottom offset.
 5. The method of claim 4, furthercomprising, in response to determining that the base layer was not codedbased on the first coding scheme or a coding scheme associated with thefirst coding scheme, encoding the picture based on the at least oneposition offset.
 6. The method of claim 1, wherein the base layerfurther comprises an output picture size.
 7. An apparatus for encoding apicture in a multi-layer bitstream, comprising: a memory; and a hardwareprocessor operationally coupled to the memory and configured to: encodeat least one enhancement layer of the multi-layer bitstream based on afirst coding scheme, the multi-layer bitstream comprising a base layerdifferent from the enhancement layer; determine whether the base layerwas coded based on the first coding scheme or a coding scheme associatedwith the first coding scheme; encode a conformance window flag in aVideo Parameter Set (VPS) of the base layer, wherein the conformancewindow flag indicates whether the VPS comprises at least one positionoffset, the at least one position offset indicative of positioninginformation for the picture; and in response to determining that thebase layer was coded based on the first coding scheme or a coding schemeassociated with the first coding scheme, set the conformance window flagto a first predetermined value, or in response to determining that thebase layer was not coded based on the first coding scheme or a codingscheme associated with the first coding scheme: (i) set the conformancewindow flag to a second predetermined value different from the firstpredetermined value, the second predetermined value indicating the VPScomprises the at least one position offset, and (ii) encode the at leastone position offset in the VPS of the base layer.
 8. The apparatus ofclaim 7, wherein a coding scheme is associated with the first codingscheme only if the coding scheme is identical to the first codingscheme.
 9. The apparatus of claim 7, wherein a coding scheme isassociated with the first coding scheme only if the first coding schemeis a scalable extension of the coding scheme.
 10. The apparatus of claim7, wherein the at least one position offset comprises at least one of aleft offset, a right offset, a top offset, and a bottom offset.
 11. Theapparatus of claim 10, wherein the processor is further configured to,in response to determining that the base layer was not coded based onthe first coding scheme or a coding scheme associated with the firstcoding scheme, encode the picture based on the at least one positionoffset.
 12. The apparatus of claim 7, wherein the base layer furthercomprises an output picture size.
 13. A method for decoding a picture ina multi-layer bitstream, comprising: receiving the multi-layerbitstream, the multi-layer bitstream comprising at least an enhancementlayer and a base layer; decoding a conformance window flag in a VideoParameter Set (VPS) of the base layer, the conformance window flagindicating whether the VPS comprises at least one position offset; andin response to the conformance window flag being set to a predeterminedvalue, decoding at least one position offset in the VPS of the baselayer.
 14. The method of claim 13, wherein the at least one positionoffset comprises at least one of a left offset, a right offset, a topoffset, and a bottom offset.
 15. The method of claim 14, furthercomprising, in response to the conformance window flag being set to apredetermined value, decoding the picture based on the at least oneposition offset.
 16. The method of claim 13, wherein the base layerfurther comprises an output picture size.
 17. An apparatus for decodinga picture in a multi-layer bitstream, comprising: a memory; and ahardware processor operationally coupled to the memory and configuredto: receive the multi-layer bitstream at a video codec, the multi-layerbitstream comprising at least an enhancement layer and a base layer;decode a conformance window flag in a Video Parameter Set (VPS) of thebase layer, wherein the conformance window flag indicates whether theVPS comprises at least one position offset; and in response to theconformance window flag being set to a predetermined value, decode theat least one position offset in the VPS of the base layer.
 18. Theapparatus of claim 17, wherein the at least one position offsetcomprises at least one of a left offset, a right offset, a top offset,and a bottom offset.
 19. The apparatus of claim 18, wherein theprocessor is further configured to, in response to the conformancewindow flag being set to a predetermined value, decode the picture basedon the at least one position offset.
 20. The apparatus of claim 17,wherein the base layer further comprises an output picture size.